## DEV Community

LP

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# Variables & Strings

Variables are used to store values. A string is a series of characters, surrounded by single or double quotes.

Hello world

print("Hello world!")

Hello world with a variable

msg = "Hello world!"

print(msg)

# Concatenation (combining strings)

first_name = 'albert'

last_name = 'einstein'

full_name = first_name + ' ' + last_name print(full_name)

# Lists

A list stores a series of items in a particular order. You access items using an index, or within a loop.

#### Make a list

bikes = ['trek', 'redline', 'giant']

#### Get the first item in a list

first_bike = bikes

#### Get the last item in a list

last_bike = bikes[-1]

#### Looping through a list

for bike in bikes:

print(bike)

#### Adding items to a list

bikes = []
bikes.append('trek')
bikes.append('redline')

bikes.append('giant')

#### Making numerical lists

squares = []
for x in range(1, 11):

squares.append(x**2)

#### List comprehensions

squares = [x**2 for x in range(1, 11)]

#### Slicing a list

finishers = ['sam', 'bob', 'ada', 'bea'] first_two = finishers[:2]

#### Copying a list

copy_of_bikes = bikes[:]

# Tuples

### Tuples are similar to lists, but the items in a tuple can't be modified.

#### Making a tuple

dimensions = (1920, 1080)

# If Statements

### If statements are used to test for particular conditions and respond appropriately.

##### Conditional tests

equals x == 42
not equal x != 42
greater than x > 42
or equal to x >= 42
less than x < 42
or equal to x <= 42

#### Conditional test with lists

'trek' in bikes
'surly' not in bikes

#### Assigning Boolean values

game_active = True
can_edit = False

#### A simple if test

if age >= 18:
print("You can vote!")

### If-elif-else statements

if age < 4:
ticket_price = 0
elif age < 18:
ticket_price = 10
else:

ticket_price = 15

# Dictionaries

#### A simple dictionary

alien = {'color': 'green', 'points': 5}

#### Accessing a value

print("The alien's color is " + alien['color'])

#### Adding a new key-value pair

alien['x_position'] = 0

#### Looping through all key-value pairs

fav_numbers = {'eric': 17, 'ever': 4} for name, number in fav_numbers.items():

print(name + ' loves ' + str(number))

#### Looping through all keys

fav_numbers = {'eric': 17, 'ever': 4} for name in fav_numbers.keys():

print(name + ' loves a number')

#### Looping through all the values

fav_numbers = {'eric': 17, 'ever': 4}

for number in fav_numbers.values():

print(str(number) + ' is a favorite')

# UserInput

#### Prompting for a value

name = input("What's your name? ")
print("Hello, " + name + "!")

Prompting for numerical input

age = input("How old are you? ")
age = int(age)

pi = input("What's the value of pi? ")
pi = float(pi)

# While-Loops

A while loop repeats a block of code as long as a certain condition is true.

# A simple while loop

current_value = 1

while current_value <= 5:

print(current_value)

current_value += 1

#### Letting the user choose when to quit

msg = ''

while msg != 'quit':

msg = input("What's your message? ")

print(msg)

# Functions

#### A simple function

def greet_user():
"""Display a simple greeting."""
print("Hello!")

greet_user()

#### Passing an argument

"""Display a personalized greeting."""

print("Hello, " + username + "!")

greet_user('jesse')

#### Default values for parameters

def make_pizza(topping='bacon'):

"""Make a single-topping pizza.""" print("Have a " + topping + " pizza!")

make_pizza()
make_pizza('pepperoni')

#### Returning a value

"""Add two numbers and return the sum."""
return x + y

print(sum)

# Class

#### Creating a dog class

class Dog():

"""Represent a dog."""

def init(self, name):

"""Initialize dog object."""

self.name = name

def sit(self):

"""Simulate sitting.""" print(self.name + " is sitting.")

my_dog = Dog('Peso')

print(my_dog.name + " is a great dog!")

my_dog.sit()

#### Inheritance

class SARDog(Dog):

"""Represent a search dog."""

def init(self, name):

"""Initialize the sardog."""

super().init(name)

def search(self):

"""Simulate searching.""" print(self.name + " is searching.")

my_dog = SARDog('Willie')

print(my_dog.name + " is a search dog.")

my_dog.sit()

my_dog.search()

I
Reading a file and storing its lines

# Working With Files

filename = 'LP.txt'

with open(filename) as file_object: lines = file_object.readlines()

for line in lines:

print(line)

#### Writing to a file

filename = 'journal.txt'

with open(filename, 'w') as file_object:

file_object.write("I love programming.")

#### Appending to a file

filename = 'journal.txt'

with open(filename, 'a') as file_object:

file_object.write("\nI love making games.")

# Exception Handling

#### Catching an exception

prompt = "How many tickets do you need? "
num_tickets = input(prompt)

try:
num_tickets = int(num_tickets)
except ValueError: